Oscillator



Feb. 6, 1934. w HA EL 1,945,546

OSCILLATOR Filed Oct. 18, 1929 ("I "6"" ""6656 ll QNTENNQ INVENTORCLARENC E W. HANSELL' BY vf dm ATTORN EY Patented Feb. 6, 1934 PATENToFEicE oscmm'roa 1 Clarence W. Hansell, PortJeifer-uon, N. Y., as-

aignor to Radio Corporation of America, a eor-' porationof DelawareApplication October 1S, 1929. Serial No. 400,489 2': Claims. (01.250-36) l lators of which the most effective have been mechanicaloscillators, such as tuning forks and piezo-electric quartz crystals,which control the output frequency of a generator through a chain ofamplifiers. However, these schemes offer the disadvantages that they-areexpensive, difficult to adjust and add greatly to the probability offailures in service due to the increase in the number of tubes, circuitsetc., the failure of any one of which may interrupt the operation of theequipment.

In order to eliminate the foregoing difficulties, another object of thisinvention is to provide an oscillator in which low power frequencycontrol devices such as crystals and their associated low poweramplifiers and circuits may be eliminated, and wherein frequencystabilization may be applied directly to a relatively high powergenerator of oscillations.

Broadly, to accomplish this object I make use of a sharply tuned circuitcoupled to the high frequency oscillator which reacts upon theoscillator in a way which tends to hold the oscillator frequency near tothe resonant frequency of the circuit. For the purpose of obtaining avery sharply tuned circuit, and to have afrequency control circuit whichshall be independent of the load taken from the oscillator, I make useof a long resonant line having substantially uniformly distributedinductance and capacity.

Further, I cause such a line to have standing waves built up thereondepending solely upon the frequency and the length of the line andindependent of any reaction caused by external circuits or loads, and,according to my invention, I apply the standing waves produced on theline to the generator, which I preferably make a tube oscillator, forcontrolling the frequency of oscillation thereof. In this way, not onlydoes the long line act as a resonant circuit to pull the oscillator intostep therewith; but, in another aspect it can be considered as a phaseshifter, waves from the oscillator being sent over the line to the farend and reflected back to the oscillator, arriving back with a phasewhich shifts rapidly with change of frequency and which tends to modifythe oscillator frequency to make zero difference in phase between theingoing and reflected waves at the input end of the line. That is tosay, the long line acts to pull the oscillator. into phase with its ownoscillations whenever there is a shift in phase caused by shift in theoscillator frequency.

Still other objects of my invention are to provide a frequencystabilizer which improves in accuracy as the frequency at which it isoperated '65 is increased, and to provide a frequency. stabilizer whichshall be independent of variations in temperature humidity andbarometric pressure. These objects are also fulfilled by the provisionof' a long line for frequency control. As frequency increases, thelength of any particular line, expressed in wave lengths, increases inpro-, portion to frequency. Since the rate of phase shift in thereflected waves with change of frequency is proportional to the numberof wave 76 lengths in the line it follows that the theoreticalpercentage accuracy obtainable with any particular line increases inproportion to the frequency at which it is operated.

With reference to the last mentioned objects, 80 they are accomplishedby temperature controlling the line; or, by designing the line so as tohave constant electrical length regardless of temperature, by usingmaterials not affected by humidity and placing the line in a sealedcontainer. The effect of barometric pressure which may have considerableeffect on the frequency of a crystal has practically no effect on aline. The effect of vibration is made negligible by using a rigid lineconstruction.

Still another object of my invention is to provide a frequencystabilizer which may be utilized to stabilize an oscillator at more thanone frequency, or in other words, to provide a stabilizer readilyadapted to frequency changeover. This object is also accomplished by theuse of a long resonant line, for, by simply varying the length of theline, the wave length of the standing waves thereon may readily bechanged. Or, if desired, the line may be made to resonate at and to havenot only standing waves of a fundamental frequency thereon, but alsowaves corresponding to harmonic frequencies relative to its fundamental.

The invention may best be understood by referring to the accompanyingdrawing in which I have shown a few embodiments of my invention which,of course, are to be taken only by way of illustration and not by way oflimitation.

In the accompanying drawing, Figure '1 .indi-' no cates a resonant lineinductively coupled to a tube oscillator for frequency control thereof,

Figure 2 indicates similar apparatus to tha shown in Figure 1 butwherein the line is capacitively connected or coupled to an oscillator,

Figure 3 shows by way ofexample a pushpull transmitter having, accordingto my invention, a long line directly connected or coupled thereto forfrequency control, and,

Figure 4 is similar to Figure 3 but shows, in addition, an amplifierafter the frequency controlled oscillator.

Tuming to Figure 1 I have indicated a high power tube oscillator 1having in its output circuit a tunable circuit 2 tuned to approximatelyor as nearly as possible to a desired frequency, In this manner, thetuned circuit acts as a relatively rough controlfor the oscillatorfrequency. The control electrode 3 of tube 1 is regeneratively connectedto the output circuit. Resistance 4 is provided to insure a correctbiasing potential and choke 5 helps prevent radio frequency losses inthe resistance. Condenser 6 acts as a radio frequency path to ground.Condenser '7 is the usual blocking condenser. Anode potential issupplied through a choke 8 to the anode 9.

The arrangement as shown is self starting and produces oscillations of afrequency corresponding to that to which circuit 2 is tuned. However, asso far described, due to a change in load upon the oscillator or due tosome external reaction upon the circuits thereof, or due to a'change involtage applied to some of the elements thereof,

. or for some other reason, the oscillation frequency of the oscillatorwill vary. Consequently, circuit 2 only approximately controls thefrequency of oscillation. I

In order to prevent variation in frequency I inductively couple to theoutput circuit 2 of the oscillator by means of a coil12, a resonant line10 whose effective length may be adjustably varied by means of a slider11. By means of slider 11 the line 10 having substantially uniformlydistributed inductance and capacity is caused to resonate very sharplyat the desired frequency. As a resonant circuit, the line pulls theoscillator constantly into step with itself, and, as the line will notresonate at, but discriminates against, wave lengths other than that towhich it is tuned, the oscillator 1 becomes frequency stabilized andwill have very-much less variation in frequency with changes alreadyreferred to which ordinarily produce large undesired frequency changes.

Due to reflection from points 13 and 14, standing waves are producedupon the line of constant wave length, depending upon the fixed lengthof the line.

As the standing waves on the wires 15, 16 of the line 10 are opposite inphase, the standing wave potentials applied to the control electrode andanode of the oscillator will have the correct phase relationship forsustained oscillation generation; and further, these potentials ofopposite phase on lines 15 and 16 will pull the alternating poj astentials on the grid and plate of tube 1, into phase with themselves,whenever there is a tendency for a shift in phase thereof due to a shiftin frequency.

- If, after the line 10 is adjusted for a certain.

frequency, tuning condenser 32 is changed so that 5 quencies aredesired, an additional adjustment of slider 11 must be made.- In eithercase, frequency changeover is relatively extremely simple.

In Figure 2, the long line 10 has its elements or conductors 15 and 16coupled or connected to the oscillator 1 by means of condensers i7, 18.These condensers will usually have suflicient dielectric capacity to actas continuous connections or short circuits for the oscillator frequencybut if they have appreciable reactance this may easily be corrected bymaking the wires 15, 16 a little longer, than would be otherwisenecessary for the production of standing waves of correct lingltlli, bymeans of slider or adjustable mem- As already pointed out, the long line10 comprising conductors 15, 16 having uniformly distributed inductanceand capacity acts as a very sharply tuned circuit coupled totheoscillator and locks the oscillator into step with the standing wavesproduced upon the conductors.

In Figure 3 I have shown my invention applied to a transmitting systemutilizing pushpull connected electron discharge devices 19, 20. Theoutput circuits thereof are broadly tuned by varying the amount ofinductance included-between the plates of the tubes. The capacity forthe output resonant circuits of these tubes is furnished by theinterelectrode capacities 21, 22 indicated by dotted lines on thedrawing. If desired, the tuning may be altered by paralleling the tubecapacities by variable condensers 60, 62 or by paralleling a portion ofthe inductance 23 with a condenser 64.

The long resonant line for stabilizing the frequency of the pushpulloscillator is directly connected to the control electrodes or grids ofthe tubes. In other words, as in Figures land 2, the long line isclosely coupled to the oscillator and carries a relatively considerableamount of high frequency energy.

Modulation or keying is accomplished by a suitable device 24 operatedeither directly or remotely. Device 24, of course, may be replaced by atelephone or a resistance through which voice or other signallingcurrents are made to flow, or, the anode potential of the oscillatortubes may be varied in accordance with methods already well known in theart.

As indicated on the drawing when keying device 24 is closed, negativebias is removed from '30 prevents short circuiting of the source ofbiasing potential 31 at that time also. Between the control electrodesor grids of tubes 19, 20 there is connected a high frequency choke coilor impedance 66, whose mid-point is grounded through a by-passingcondenser 68.

In Figure 4 I have shown an arrangement similar to that disclosed inFigure 3 but wherein the modulating currents are in the form of voicecurrents. Voice currents from telephone 50 may 7 be amplified as desiredby any suitable amplifler 51 before causing the modulation of currentsin the oscillator 19, 20. The output of the oscillator may be amplifiedin any suitable way by any desired number of amplifier stages; and, inthis case I have shown by way of example a single high power pushpullamplifier stage 52, 53 which amplifies the modulated oscillatorycurrents before transmission over the antenna system 28.

To prevent radiation from the long line, it, of course, may be, asalready stated, shielded or, the wires 15, 16 may be placed very closetogether, parallel, and, side by side as illustrated so that there ismutual radiation cancellation.

Still another way of preventing radiation would be to make -wires 15 and16 concentric. This scheme would also offer the advantage that theexternal conductor could be grounded and in this way any radiation issimply and effectively eliminated. A line controlled system making useof concentric conductors is described more fully in my copendingapplication Serial Number 534,255, filed May 1, 1931 in the UnitedStates Patent Office.

Preferably the long resonant control line is placed indoors andtemperature controlled so as not to vary in length. It may as alreadyindicated, be made of material having zero coefficient of expansionwhereby changes in length are avoided.

Although in the drawing the long line, (which is termed long because itis ordinarily a number of half wave lengths long) has been shown inconnection with a single thermionic device or oscillator, or inconnection with a single power stage, it should be apparent that, ifdesirable, a plurality of electron discharge devices or stages may beconnected in cascade and the line applied to only the first one of them.

As the line is simple in construction and can handle large currents, itcan be applied to the last stage or nearly the last stage of a poweramplifier which was not possible by the use of any frequency stabilizerheretofore known. Of course, the invention is not limited to a highpower amplifier or oscillator but may also be utilized to good advantagein low power equipment.

In actual construction, the resonant line may be an ordinarytransmission line. It is preferable, however, to keep the line indoorsto prevent variations in its electrical properties due to changes intemperature, wind, etc. Such a line is not affected by changes inbarometric pressure and humidity and, therefore, presents for frequencycontrol, marked advantage over other types of frequency control deviceswhich are sensitive to pressure and moisture changes.

Another desirable construction is one in which the line is coiled on adielectric of high strength. In this manner the line may be placedwithin an enclosure and easily temperature controlled. Also, if foundadvisable, such a line may be inclosed within a hermetically sealedcontainer which may be evacuated to any desired degree or filled withany suitable gas. Shielding of this embodiment may be accomplished bythe use of a grounded metallic cylinder about the coiled line, whichmay, if desired be split.

Having thus described my invention, what I claim is:

1. In combination, an oscillatory circuit having inductance andcapacity, an electron discharge device having an anode a cathode and agrid, connections from said anode cathode and grid to points ofdifferent alternating current potential on said oscillatory circuitwhereby oscillations are set up in said circuit at a frequencycorresponding approximately to the resonant frequency of said circuit,and, a sharply resonant circuit coupled to said oscillatory circuit formaintaining constant the frequency of oscillations generated in saidoscillatory circuit, said sharply resonant. circuit comprising a pair ofconductors having substantially uniformly distributed inductance andcapacity and arranged so as to be substantially radiationless.

2. In combination, an electron discharge device having anelectron-emitting cathode a cold electrode spaced therefrom andmaintained at a relatively positive potential and a grid intermediatesaid cold electrode and said cathode, a circuit having inductance andcapacity, connections from said electrodes to points of differentalternating current potentials on said circuit whereby oscillations areset up at a frequency corresponding approximately to the resonantfrequency of said circuit having inductance and capacity, and, a pair ofconductors, forming a sharply tuned circuit coupled to said firstmentioned circuit for maintaining the frequency of oscillations in saidcircuit having inductance and capacity substantially constant, saidconductors having uniformly distributed inductance and capacity andbeing adjusted so as to have standing waves of a desired operating wavelength built up thereon and being arranged so as to be substantiallyradiationless.

3. In combination, a pair of electron discharge devices each having anelectron emitting cathode, a cold electrode spaced therefrom and a gridintermediate said cold electrode and said cathode, a circuit havinginductance and capacity connected across said cold electrodes, means 10!supplying relatively positive potentials to said cold electrodes wherebyoscillations are set up in said circuit having inductance and capacityat a frequency corresponding approximately to the resonant frequency ofsaid circuit having inductance and capacity, and, a pair of conductorshaving substantially uniformly distributed inductance and capacityadjusted so as to have standing waves of a desired operating wave lengthset up thereon coupled to said grids whereby the oscillations in saidcircuit having inductance and capacity are substantially locked intostep at a frequency corresponding to the wave length of the standingwaves set up upon said conductors.

4. A constant frequency system comprising a pair of electron dischargedevices each having an anode a cathode and a grid, a circuit comprisingan inductance coil and a condenser connected across said anodes wherebysaid anodes fluctuate 180 degrees out of phase, an impedance connectedbetween said grids whereby saidgrids fluctuate 180 degrees out of phase,and, a pair of substantially linear conductors having substantiallyuniformly distributed inductance and capacity connected to said grids,said conductors being adjusted so as to have standing .waves set upthereon at a wave length corresponding substantially precisely to adesired frequency of operation and being arranged so as to besubstantially radiationless.

5. A vacuum tube oscillator comprising an oscillator having input andoutput circuits at least one of which is tunable and, a long line long,relative to the operating wave length having standing waves thereon ofa. desired wave length, coupled. to the oscillator so that potentials ofthe standing waves are applied thereto in such phase relationship as topull the oscillator into step therewith.

6. A pushpull tube oscillator comprising a plurality of tubes, input andoutput circuits therefor, one of said circuits having a reactive eleleament therein, and a long line several half wave lengths long at thedesired operating frequency resonant at a desired oscillation frequency,coupled thereto for controlling the frequency of 'oscillaticr. of thepushpull tube oscillator.

1 7. Radio signalling apparatus comprising a pair of pushpull connectedelectron discharge devices oscillating at a desired frequency,.andmeans, coupled to the control electrodes of said devices comprisingalong line several half wave lengths long at the desired operatingfrequency having standing waves thereonof a wave length corresponding tothe desired oscillation frequency, for stabilizing the oscillationfrequency of said oscillator.

8. A generator of constant frequency oscillations comprising amulti-electrode device having cathode grid and plate electrodes, meansfor subjecting said grid electrode to a potential such that it isnegative with respect to said cathode electrode, means for maintainingsaid plate electrode at a positive-potential with respect to saidcathode electrode, a high frequency circuit connected between said gridand cathode electrodes; a high frequency circuit connected between saidanode and cathode electrodes, one of said circuits being tuned toapproximately a desired frequency ofoperation, said circuits beingcoupled together to generate oscillations of a frequency correspondingto the tuning of said tuned circuit, and a substantially radiationlessresonant transmission line comprising a pair of straight conductorssubstantially parallel to one another and arranged close'togethercoupled to a pair of electrodes of said device for accurately frequencystabilizing the oscillations generated by said device.

9. A system for generating constant frequency oscillations comprising apair of devices each having anode cathode and grid electrodes, a highfrequency circuit connected between said anode electrodes, a highfrequency circuit connected between said grid electrodes, means forsubjecting said grid electrodes to a negative potential with respect tosaid cathode electrodes, said cathode electrodes being connectedtogether, means for subjecting said anode electrodes to a positivepotential with respect to said cathode electrodes, one of said highfrequency circuits being tuned to approximately a desired operatingfrequency, both of said high frequency circuits being coupled togetherwhereby oscillations are set up and generated at a frequencycorresponding to the tuning of said tuned high frequency circuit, asubstantially radiationless resonant transmission line comprising a pairof substantially linear conductors arranged parallel to each other andclose together coupled to a pair of electrodes of said devices forfrequency stabilizing the oscillations generated by said devices, and,an output circuit, independent of said line, coupled to the circuitconnected between said anode electrodes.

10. In apparatus for generating high frequency oscillations ofsubstantially constant frequency, a pair ofelectron discharge deviceseach having anode cathode and grid electrodes, a circuit havinginduc'ance and capacity and exhibiting parallel resonance phenomena atapproximately a desired operating wavelength connected between saidanode eletrodes whereby 'said anode electrodes fluctuate out of phase atthe desired operating frequency, a circuit connected between said anodeand cathode electrodes for subjecting said anode electrodes to asuitable operating potential with respect to said cathode electrodes, acircuit connected between said grid electrodes and said cathodeelectrodes for subjecting said grid electrodes with respect ranged as tobe substantially radiationless, said conductors being adjusted ineflZetive electrical length so as to have standing waves of a desiredoperating wavelength thereon and said conductors being'dimensioned as tobe of low loss and adapted to handle relatively large amounts ofcirculatory frequency controlling currents, and, a load output circuit,independent of said pair of conductors, coupled to said circuitconnected between said anodes. v

11. A pushpull electron discharge device oscillating system comprising apair of electron discharge devices each having an anode a cathode and acontrol electrode, an inductance coil connected between said anodes, animpedance connected between said control electrodes, a connection toground from a point intermediate said impedance, said connectionincluding a'resistance, and, a pair of conductors having uniformlydistributed inductance and capacity conductively connected to saidcontrol electrodes, said conductors being adjusted so as to havestanding waves of a wave length corresponding to a desired operatingfrequency built up thereon and 11( acting to pull the oscillationsgenerated by said electron discharge devices into step with saidstanding waves.

12. In apparatus for amplifying or sustaining undulatory high frequencycurrents, the combi- 115 nation of an electron discharge device havinginput and output electrodes, a rough frequency controlling circuithaving inductance and capacity regeneratively coupling said electrodestogether, and, a long transmission line long relative to the operatingwave length closely coupled thereto, said line comprising a pair oflinear conductors having uniformly distributed inductance and capacity,being sharply resonant to a desired operating frequency and havingstanding waves 13-5 thereon, for frequency stabilizing the undulatorycurrents regeneratively amplified or sustained by said device.

13. In combination a pair of electron discharge devices each having ananode a cathode and a 3 grid, an inductance coil connected between saidanodes, capacities between said anodes and grids acting to causeregenerative production ofoscillations at an approximately constantfrequency, and, a pair of substantially linear conductors connected tosaid grids, said conductors having substantially uniformly distributedinductance and capacity, said conductors being adjusted so as to havestanding waves set up thereon at a wave length corresponding exactly toa desired frequency of operation and acting to pull the frequency ofoscillations setup by said capacities into step with the standing wavesset up thereon.

14. A constant frequency system comprising a pair of electron dischargedevices each having an anode a cathodeand a grid, an inductance coilconnected between said anodes, a condenser connected to said inductancecoil, an impedance connected between said grids whereby said gridsfluctuate substantially 180 degrees out of phase, and,

a pair of substantially linear conductors having substantially uniformlydistributed inductance and capacity connected to said grids, saidconductors being adjusted so as to have standing waves of a desiredoperating wave length set up thereon and acting to pull the oscillationsgenerated by said devices into step with the standing waves.

15. In a system for the production of sustained high frequencyoscillations of substantially constant wave length, an oscillator forthe generation of high frequency oscillations comprising an electrondischarge device having regeneratively coupled input and outputelectrodes, a tuned circuit for controlling the frequency ofoscillations generated to approximately a desired value, and, a two wireradiationless transmission line long, relative to the operating wavelength having standing waves thereon of a wave length corresponding to adesired frequency of oscillation, closely coupled to said oscillator forpulling the oscillations generated by said oscillator into step with thestanding waves on the transmission line.

16. In a system for the production of high frequency oscillatory energy,a regeneratively acting electron discharge device utilizinginterelectrode capacity for the production of sustained oscillations,reactive tuning means for roughly controlling the frequencv ofoscillations generated by said electron discharge device, and, a longresonant transmission line, long relative to the operating wave lengthhaving standing waves thereon of a wave length corresponding to adesired frequency of oscillation, coupled to said oscillator so that theoscillations generated thereby are pulled into step with the standingwaves on said resonant long line.

17. In a system for the generation of sustained high frequencyundulatory electrical currents, a

' pair of pushpull connected electron discharge devices utilizing forfeed back the grid-plate capacities of said devices, a rough frequencycontrolling circuit connected across the plates of said pushpullconnected devices, said circuit comprising an .inductance coil and avariable condenser connected in shunt with a portion of said coil, and,a long resonant radiationless transmission line -long, relative to theoperating wave length having standing waves thereon, coupled thereto sothat the undulatory currents generated by said pushpull connectedelectron discharge devices correspond in frequency to the standing waveson said line.

18. A constant frequency oscillation generator comprising an electrondischarge device having an anode a cathode and a control electrode, atuned circuit comprising an inductance coil and a condenser, meanscoupling said anode cathode and control electrode to said tuned circuitwhereby oscillations are set up, and, a long transmission line, long,relative to a desired wave length, closely coupled to said oscillatingsystem com-prising said tuned circuit and said electron dischargedevice, waves fed into the line being reflected back with a shift inphase corresponding to the number of waves contained in the line wherebythe reflected waves force the oscillator to oscillate at a frequency forwhich there is zero difference in phase at the input end of the line forthe reflected wave and the ingoing wave.

19. An oscillatory system for generating oscillations of constantfrequency comprising an electron discharged device having within anhermetically sealed container -an anode a cathode and a controlelectrode, a parallel tuned circuit comprising an inductance coilshunted by a variable condenser, connections from said anode cathode andcontrol electrode to points of different alternating current potentialson said variable tuned circuit whereby oscillations correspondingroughly in frequency to a desired frequency of operation are generatedby said electrondischarge device, and, a long transmission line,consisting of a pair of conductors, having uniformly distributedinductance and capacity and being sharply resonant to a desiredoperating frequency closely coupled to electrodes-of said oscillatingdevice, whereby standing waves on said line pull the oscillatory systeminto oscillation at a frequency corresponding substantially exactly in adesired frequency of operation.

20. Means for generating oscillations compris-. ing a reactance, anelectron discharge device having an anode a cathode and a controlelectrode, connections from said reactance to said electrodes wherebyoscillations corresponding roughly in frequency to a desired frequencyare set up by said electron discharge device and reactance, and, a longtransmission line, long, relative to a desired wave length, closelycoupled to said oscillatory system comprising said electron dischargedevice and reactance, whereby standing waves on said long transmissionline pull said oscillatory system comprising said electron dischargedevice and reactance into step with the standing waves on said longtransmission line.

21. Means for generating oscillations comprising an inductance coil, anelectron discharge device comprising anv anode a cathode and a controlelectrode coupled to said inductance coil whereby oscillations aregenerated by said electron discharge device, and means, comprising along resonant transmission line, long, relative to a desired operationwave length, closely coupled to said oscillatory system comprising saidinductance coil and electron discharge device, whereby standing waves onsaid long transmission line pull said oscillatory system into steptherewith.

22. An oscillatory system comprising a pair of electron dischargedevices each having an anode a cathode and a control electrode;inductors connected between the anodes and control electrodes of saiddevices, whereby oscillations are generated by said electron dischargedevices, and, a long transmission line, long, relative to the operatingwave length coupled to the control electrode circuit of said electrondischarge devices, whereby standing waves upon said long resonanttransmission line cause said devices to oscillate at a frequencycorresponding to the wave length of the standing waves upon said longresonant transmission line.

23. An oscillatory system comprising an elec- 'tron discharge devicehaving an anode a cathode and control electrode, a parallel tunedcircuit comprising an inductance coil and a variable condenser connectedto said anode cathode and control electrode whereby oscillations aregenerated by said electron discharge device, and, a long transmissionline, long, relative to a desired operating wave length, inductivelycoupled to the inductance of said parallel tuned circuit, standing wavesset up upon said line by virtue of the close coupling, pulling theoscillations generated by said device into step with the standing waveson the line.

24. Apparatus as'claimed in the preceding claim wherein an intermediatepoint of said inductance coil forming part of said tuned circuit isgrounded for high frequency currents and connected to said cathode, andpoints on said coil opposite said grounded point being connected to saidcontrol grid and anode, and, means comprising the series combination ora choke coil and resistance connected between said cathode and controlgrid, for maintaining suitable biasing potential on said grid withrespect to said cathode.

25. In an oscillating system comprising an electron discharge devicehaving ananode a cathode and a control electrode, a tunablecircuitcomprising an inductance coil and a variable condenser connectedin parallel therewith, the coil to said tunable circuit being connectedat an intermediate point to said cathode and at points on both sides ofsaid point to said control grid and anode, whereby oscillations aregenerated by said electron discharge device, means for grounding said'point and said cathode for high frequency currents, means forestablishing suitable grid bias upon the control grid of said electrondischarge device, and, a long resonant transmission line, long, relativeto a desired operating wave length, closely coupled to said paralleltuned circuit through relatively large blocking condensers offering noappreciable impedance tooscillatory energy of a frequency generated bysaid electron discharge device whereby standing waves set up on saidresonant long line due to its close coupling with the electron dischargedevice oscillator, pulls the oscillator into step in frequency at afrequency corresponding to the wave length of the standing waves on thelong line.

26. A pushpull electron discharge device oscillating system comprisinga'pair of electron discharge devices each having an anode a cathode anda control electrode, an inductor connected between said anodes, another.inductor connected between said control electrodes, means for groundingthe midpoint oi said last mentioned inductor, and, a long transmissionline, long, relative to a desired wave length, conductively coupled tosaid control electrode inductor at points on both sides of said groundedmidpoint, whereby standing waves on said long resonant transmission linepull the oscillations generated by said electron discharge devices intostep therewith.

27. Apparatus as claimed in the preceding claim wherein a unidirectionalpotential path to ground from the midpoint of said control electrodeinductor is provided, and wherein the effective resistance of said pathis altered in accordance with desired modulation, whereby the output ofsaid oscillator is modulated in accordance with said modulation.

' CLARENCE W. HANSELL.

